CN114221335A - Control method for generator-network-following type MMC converter station parallel power supply system - Google Patents

Control method for generator-network-following type MMC converter station parallel power supply system Download PDF

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CN114221335A
CN114221335A CN202111537028.5A CN202111537028A CN114221335A CN 114221335 A CN114221335 A CN 114221335A CN 202111537028 A CN202111537028 A CN 202111537028A CN 114221335 A CN114221335 A CN 114221335A
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network
controller
mmc
constant
outer ring
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CN114221335B (en
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项中明
倪秋龙
李振华
徐建平
周正阳
周靖皓
吕勤
胡济恒
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State Grid Zhejiang Electric Power Co Ltd
Jinhua Power Supply Co of State Grid Zhejiang Electric Power Co Ltd
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State Grid Zhejiang Electric Power Co Ltd
Jinhua Power Supply Co of State Grid Zhejiang Electric Power Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/002—Flicker reduction, e.g. compensation of flicker introduced by non-linear load
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/04—Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
    • H02J3/06—Controlling transfer of power between connected networks; Controlling sharing of load between connected networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Control Of Eletrric Generators (AREA)

Abstract

The invention discloses a control method for a parallel power supply system of a generator-network-following type MMC converter station, which adopts improved reactive constant alternating voltage control, and inhibits the low-frequency oscillation instability phenomenon of the system caused by the access of the traditional network-following type MMC converter station by adding an advanced correction auxiliary control link to a q-axis outer ring controller of the network-following type MMC converter station, thereby ensuring the synchronous and stable operation of the power supply system and a power grid. The invention adopts parallel feedforward control, and ensures that the fault transient operation characteristic of the network-following MMC is unchanged by arranging an amplitude limiting link on an additional branch. After the method is used, the low-frequency oscillation instability phenomenon of the system is successfully inhibited, the advanced auxiliary controller has good robustness, and the method is applicable to the q-axis outer ring controller of the network-following MMC when the parameters of the q-axis outer ring controller change within a certain range.

Description

Control method for generator-network-following type MMC converter station parallel power supply system
Technical Field
The invention belongs to the technical field of power transmission and distribution of a power system, and particularly relates to a control method for a parallel power supply system of a generator and a network-following type MMC converter station.
Background
With the rapid development of power electronic devices, a voltage source converter based flexible direct current (VSC-HVDC) technology is also widely used. Compared with a traditional direct current system based on a semi-controlled device, the VSC-HVDC has the advantages of being flexible in control, free of phase change voltage provided by a power grid, capable of independently controlling active power and reactive power, capable of providing synchronous alternating current power supply support for a passive network and the like, has the advantages of supplying power to the passive network, independently controlling the active power and the reactive power, capable of flexibly achieving trend reversal and the like, is widely applied to scenes of new energy grid connection, interconnection among alternating current large power grids, offshore wind power access, direct current power distribution networks and the like, and is huge in development prospect. The modular multilevel converter MMC has the advantages that harmonic components are few, the power device series connection technology is not needed, and the like, and becomes a preferred voltage source converter in large-scale new energy base grid connection. Meanwhile, MMC-HVDC is used as an important asynchronous machine power supply, and can replace a synchronous machine power supply to supply power to a system in a future power system.
When the MMC-HVDC is used as an asynchronous machine power supply, two typical control strategies of a network following type and a network construction type are mainly adopted. The network-forming MMC controls the amplitude and the phase of the voltage of the grid-connected point, can simulate the inertia and the damping characteristic of a generator, and has unique advantages when supplying power to a passive network; the network following MMC usually adopts current vector control, an outer ring controller realizes decoupling control of active/passive quantity, an active control ring usually fixes active power, a reactive ring can adopt a fixed reactive power/alternating voltage control strategy, a Phase Locked Loop (PLL) is adopted to track voltage of a grid-connected point, synchronization with an active power grid is realized, and the network following MMC has a better damping characteristic when the strength of an access system is higher.
With the increase of the demand of electric energy and the increase of environmental protection pressure, the demand of clean energy is continuously increased, and the leading position of the power supply of the traditional synchronous machine is broken in the future; as the synchronous machine power supply is gradually replaced by the non-synchronous machine power supply, the power supply system with the generator connected in parallel with the MMC converter station becomes an important power supply mode. Compared with a network-type MMC, the network-following type MMC has good damping characteristic when being connected into a strong system, so that the generator-network-following type MMC parallel power supply system has stronger synchronous stability when being merged into an alternating current power grid; when adopting with the reactive ring of net type MMC and deciding alternating voltage control, thereby alternating current system takes place when serious failure with net type MMC can provide reactive support fast and promote voltage recovery, promote system transient stability. For the generator-network-following type MMC converter station parallel power supply system shown in FIG. 1, a generator is connected with a grid-connected point of a network-following type MMC through an alternating current transmission line, and the generator and the network-following type MMC converter station are connected in parallel through the alternating current transmission line to transmit power to a power grid together; under this scene, follow net type MMC's q axle and decide alternating voltage controller and can exert an influence to the damping characteristic of generator, lead to the system to take place the low frequency oscillation unstability, be unfavorable for system steady operation. Therefore, additional research into control strategies for network-following type MMC converter stations for power supply systems in parallel with generators is needed to achieve future stable and reliable power supply to the grid with generator-network-following type MMC parallel power supply systems.
Disclosure of Invention
In view of the above, the present invention provides a control method for a parallel power supply system of a generator-grid-following type MMC converter station, which can eliminate negative damping torque of a generator caused by the connection of a grid-following type MMC, ensure that the system does not have low-frequency oscillation instability, have good robustness, and simultaneously, do not affect the transient operation characteristics of the power supply system during the fault period.
A control method for a generator-network-following type MMC converter station parallel power supply system adopts a constant alternating voltage and constant active power control strategy for network-following type MMC in the system, and an advanced correction auxiliary control link is added in a q-axis outer ring constant voltage controller, namely, firstly, the maximum advanced phase provided by the auxiliary control link is determined according to the leading low-frequency oscillation frequency of a generator, then, the advance time constant, the lag time constant and the gain constant of the q-axis outer ring constant voltage controller are determined according to the maximum advanced phase, finally, the auxiliary control link is changed into a parallel connection mode, and an amplitude limiting link is added on an additional branch to ensure that the performance of the network-following type MMC is kept unchanged during a fault transient state.
Furthermore, the q-axis outer ring constant voltage controller adopts US ref-USThe result is sequentially subjected to an advanced correction auxiliary control link and an outer ring PI controller to obtain an MMC output current q-axis instruction value isqrefAnd then i will besqrefMMC output current d-axis instruction value i generated by d-axis outer ring constant power controllersdrefAs a reference value for the MMC inner-loop current controller, where US refFor grid-connected point voltage reference, USIs the MMC grid-connected point voltage amplitude.
Further, the transfer function expression of the advanced correction auxiliary control link is as follows:
Figure BDA0003407092540000031
wherein: gC(s) is the transfer function of the lead correction auxiliary control element, KcIs a gain constant, T and β T are respectively a lead time constant and a lag time constant, β is a lag coefficient, and s is laplacian.
Further, the advanced correction auxiliary control link is formed by connecting an original branch and an additional controller in parallel, namely GC(s)＝GX(s)+1，GC(s) is the transfer function of the lead corrected auxiliary control element, GX(s) is the transfer function of the additional controller, expressed as follows:
Figure BDA0003407092540000032
wherein: kcIs a gain constant, T and β T are respectively a lead time constant and a lag time constant, β is a lag coefficient, and s is laplacian.
Further, the lead time constant T, the lag coefficient beta and the gain constant KcThe calculation expression of (a) is as follows:
Figure BDA0003407092540000033
Figure BDA0003407092540000034
Figure BDA0003407092540000035
wherein: omegacIs the dominant angular frequency of oscillation of the generator,
Figure BDA0003407092540000036
the most advanced phase.
Further, the maximum advance phase
Figure BDA0003407092540000037
The calculation expression of (a) is as follows:
Figure BDA0003407092540000038
Figure BDA0003407092540000039
wherein: f. ofcIs the dominant oscillation frequency of the generator, KvAnd TvRespectively a proportional coefficient and an integral coefficient of the outer loop PI controller,
Figure BDA00034070925400000310
for outer loop PI controllers at fcLagging phase provided at the frequency point.
Further, the amplitude limiting element is used for limiting the amplitude of the additional controller, and the output of the additional controller is limited to be-0.02 p.u. to 0.02p.u.
Compared with the prior art, the invention has the following beneficial technical effects:
1. the invention provides a feasible control strategy for the parallel power supply system of the generator-network-following type MMC converter station, can avoid the phenomenon of low-frequency oscillation instability caused by adopting a network-following type MMC access system controlled by a reactive constant alternating voltage, ensures the synchronous and stable operation of the power supply system and a power grid, and plays a certain guiding role in the design of future engineering.
2. According to the invention, an advanced correction auxiliary controller is introduced into a q-axis outer ring controller of a following network type MMC, and the design of the controller is only related to the leading oscillation frequency of the system and q-axis outer ring controller parameters of the MMC and is not influenced by generator parameters and network parameter structures; the method of the invention does not need to add extra devices, is simple to implement and has good economic benefit.
3. When the q-axis outer ring controller parameters of the network-following MMC change, the leading oscillation frequency of the system also changes, and the set advanced correction auxiliary controller parameters are kept unchanged, so that the low-frequency oscillation instability phenomenon of the system can not occur when the q-axis outer ring controller parameters change within a certain range; therefore, the method has strong robustness, wide application range and extremely high engineering value.
4. When the output power instruction value of the network-following type MMC changes, the output power of the network-following type MMC can quickly follow the instruction value, and the system is ensured not to generate low-frequency oscillation instability; therefore, the method has strong applicability and great practical engineering significance.
5. When a short-circuit fault occurs at a grid-connected bus of the grid-following type MMC, the parallel power supply system can realize fault ride-through, the system can recover to stably operate after the fault is cleared, and the transient characteristic of the grid-following type MMC is kept unchanged compared with the condition that an auxiliary control strategy is not adopted; therefore, the method is simple to implement, has strong applicability under various working conditions, and has great practical engineering significance.
Drawings
Fig. 1 is a schematic diagram of a topology structure of a generator-network-following type MMC converter station parallel power supply system.
FIG. 2 is a schematic diagram of the network-following MMC outer loop control using the advanced calibration auxiliary controller according to the present invention.
Fig. 3 is a waveform diagram of rotor angular frequency of the generator under the condition that the integral constant of the q-axis outer ring controller of the network-following type MMC is changed when the auxiliary controller is not adopted.
FIG. 4 is a waveform of the angular frequency of the rotor of the generator when the parameters of the q-axis outer loop controller are changed while the parameters of the auxiliary controller are kept unchanged after the control method of the present invention is adopted.
FIG. 5 is a waveform diagram of power delivered by an MMC converter station when a power command value of a net-type MMC converter station is changed by using the control method of the present invention.
FIG. 6 is a d-axis and q-axis current waveform diagram of MMC under the condition that three-phase metallic grounding short circuit fault occurs at a grid-connected point bus of a net-type MMC converter station after the control method of the present invention is adopted.
Detailed Description
In order to more specifically describe the present invention, the following detailed description is provided for the technical solution of the present invention with reference to the accompanying drawings and the specific embodiments.
As shown in fig. 2, the control strategy for the generator-grid-following type MMC converter station parallel power supply system of the present invention includes the following steps:
(1) for a network-following MMC current converter, an improved constant alternating voltage control strategy is adopted in a reactive power control link, and an advanced correction auxiliary control link is added into a q-axis outer ring controller.
Setting a q-axis outer-loop controller of a network-following MMC to control the voltage amplitude of a grid-connected point alternating-current bus, and adding a feedforward advanced correction controller GCThe transfer function of (a) is of the form:
Figure BDA0003407092540000051
(2) for a generator-network-following type MMC parallel power supply system, the maximum leading phase provided by an auxiliary controller is firstly determined according to the dominant low-frequency oscillation frequency of a generator.
If feedforward control is not adopted, the dominant oscillation frequency of the generator is fcAnd q-axis outer ring controller G of net-following type MMCvRespectively, is Kv、TvQ-axis outer ring controller G of following net type MMCvAt fcAt the provided lagging phase
Figure BDA0003407092540000052
Comprises the following steps:
Figure BDA0003407092540000053
accordingly, the lead correction controller G is determinedc(s) maximum lead phase provided
Figure BDA0003407092540000054
Comprises the following steps:
Figure BDA0003407092540000055
(3) and for the network following type MMC current converter, the lead time constant, the lag time constant and the gain constant of the controller are determined according to the maximum lead phase.
Let advance correct the controller Gc(s) lead and lag time constants of T and beta T, respectively, and a controllerGain coefficient K ofcAccording to the maximum lead phase
Figure BDA0003407092540000056
And dominant oscillation angular frequency ωcCalculating parameters T, beta and K, respectivelyc：
Figure BDA0003407092540000061
Figure BDA0003407092540000062
Figure BDA0003407092540000063
(4) For the network-following MMC current converter, a parallel advanced correction controller is adopted, and an amplitude limiting link is added on an additional branch to ensure that the performance of the network-following MMC is kept unchanged during the fault transient state.
The calculated lead correction controller Gc(s) is changed into a parallel connection mode, and the two parallel branches are respectively an original branch and an additional controller GX(s), namely:
GC(s)＝GX(s)+1
Figure BDA0003407092540000064
in the additional controller GXThe limiting link is arranged on the(s), and the maximum output and the minimum output of the limiting link are limited to 0.02p.u. and-0.02 p.u., so that the G is ensured to be in case of serious system failureX(s) will reach the clipping value very quickly.
The output result of the outer ring voltage controller is used as the reference value of the MMC inner ring current controller, the design method of the inner ring current controller is basically the same as that of the inner ring current controller of the traditional MMC, and the maximum output and the minimum output of the MMC inner ring current amplitude limiting link can be limited to be near 1.2p.u. and-1.2 p.u.
The generator-network-following type MMC parallel power supply system adopted in the embodiment is shown in fig. 1, wherein a generator is connected with a grid connection point of an MMC through an alternating current transmission line and is connected to a power grid through another transmission line in a parallel connection mode; the rated capacity of the generator is 400MVA, the rated transmission power of the MMC converter station is 400MW, the rated direct-current voltage is 400kV, and the specific parameters of a main loop of the system are shown in Table 1.
TABLE 1
Figure BDA0003407092540000065
Figure BDA0003407092540000071
(1) In a steady-state operation state, the following network type MMC adopts a control mode that a d-axis outer ring controller determines active power and a q-axis outer ring controller determines a grid-connected point alternating-current voltage amplitude. As shown in FIG. 2, wherein Ps refOutputting an active power reference value, P, for the MMCsOutputting actual value of active power, U, for MMCs ref、UsReference and actual values of the grid-connected point voltage, isdref、isqrefReference values of d-axis and q-axis components, G, of MMC output currentpDetermining an active power controller transfer function for a d-axis of the MMC; the output active power of the generator is 200MW, the MMC operates as an inverter station, and the output active power is 200 MW. In the initial state, the proportion/integral constant of the q-axis outer ring controller of the MMC is selected as Kv＝0.8，TvAt 0.05, the system generates low-frequency oscillation with the dominant frequency of 0.9 Hz. An advance correction auxiliary control is adopted in a q-axis outer ring controller of a following network type MMC as shown in fig. 2, and parameters T1.55, beta 0.013 and K are obtained through parameter settingc＝0.114。
(2) With parallel form of lead correction control, additional controller GX(s) the expression is:
Figure BDA0003407092540000072
in the additional branch GXAnd(s) a limiting link is arranged, and the maximum output and the minimum output of the limiting link are limited to 0.02p.u. and-0.02 p.u.. The output result of the outer ring voltage controller is used as the reference value of the MMC inner ring current controller, the design method of the inner ring current controller is basically the same as that of the inner ring current controller of the traditional MMC, and the maximum output and the minimum output of the MMC inner ring current amplitude limiting link are limited to be near 1.2p.u. and-1.2 p.u.
(3) Under the condition of adopting a traditional control strategy, the following network type MMC adopts a control mode that a d-axis outer ring controller fixes active power and a q-axis outer ring controller fixes a grid-connected point alternating-current voltage amplitude, and at the moment, an integral constant T of the MMC, which fixes the q-axis outer ring controller, is changedv0.01,0.03 and 0.15 respectively, and the rotor angular frequency waveform of the generator is shown in fig. 3.
(4) Under the condition of adopting the control strategy of the invention, the q-axis outer ring controller of the following network type MMC is added with advanced correction auxiliary control, and the controller parameters are set according to the steps (1) to (2). At the moment, the integral constant T of the q-axis outer ring controller of the MMC is changedv0.03, 0.05 and 0.15 respectively, and T is equal to T adopting the traditional control strategyvIn comparison with a 0.05-hour grid-type MMC, the rotor angular frequency waveform of the generator is shown in fig. 4.
(5) And the simulation of the power step is carried out under the condition of adopting the control strategy of the invention. At the 10 th s, the power command value of the network-following type MMC is set to be increased from 0.5p.u. to 0.55p.u., and at the 12 th s, the power command value of the MMC is set to be decreased from 0.55p.u. to 0.5p.u., and the power reference value is selected to be 400MW, so that the actual output power waveform of the MMC is as shown in fig. 5.
(6) Under the condition of adopting the control strategy, for the simulation of the fault, the three-phase metallic grounding short circuit fault at the grid-connected point of the grid-following type MMC is set, and the fault duration is 0.1 s; compared with the net-following type MMC adopting the traditional control strategy, the waveforms of d-axis and q-axis components per unit values of the output current are shown in FIG. 6.
For the above example, as can be seen from fig. 3 and 4, when using a transmitterWhen the system is in a control mode, the generator rotor can generate low-frequency oscillation when T is measuredvAt 0.03, 0.05 and 0.15, the damping torque of the generator is negative and the system may exhibit low frequency oscillation instability. When the network-following MMC adopts the control strategy of the invention, the damping torque of the generator is changed from negative to positive, and the low-frequency oscillation instability phenomenon of the system can not occur, thus proving the effectiveness of the auxiliary control strategy adopted by the invention in the aspect of inhibiting the low-frequency oscillation of the system. And the simulation result of fig. 4 shows that, under the condition of adopting the well-defined and unchanged advanced correction auxiliary controller parameters, the q-axis outer ring controller parameters of the network-following type MMC are changed within a certain range, and the low-frequency oscillation instability of the system can be avoided by adopting the auxiliary control strategy, so that the control method of the invention has good robustness and adaptability. The simulation result of fig. 5 shows that when the MMC power command value changes, its output power can track the command value without deviation, the response characteristic is quick, and the system can be kept running stably. The simulation results of fig. 6 illustrate that the generator-grid-type MMC parallel power supply system is able to ride through the most severe three-phase metallic short-circuit fault, and it can be seen that the response characteristics of the MMC employing the conventional control method and the control strategy of the present invention are almost the same during the fault transient, illustrating that the auxiliary control strategy employed by the present invention does not affect the response characteristics during the system fault transient. The above simulation results illustrate the effectiveness of the present invention.
The embodiments described above are presented to enable a person having ordinary skill in the art to make and use the invention. It will be readily apparent to those skilled in the art that various modifications to the above-described embodiments may be made, and the generic principles defined herein may be applied to other embodiments without the use of inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications to the present invention based on the disclosure of the present invention within the protection scope of the present invention.

Claims (8)

1. A control method for a generator-network-following type MMC converter station parallel power supply system is characterized by comprising the following steps: a constant alternating voltage and constant active power control strategy is adopted for a network following type MMC in a system, and an advanced correction auxiliary control link is added into a q-axis outer ring constant voltage controller, namely, the maximum advanced phase provided by the auxiliary control link is determined according to the dominant low-frequency oscillation frequency of a generator, the advance time constant, the lag time constant and the gain constant of the q-axis outer ring constant voltage controller are determined according to the maximum advanced phase, the auxiliary control link is changed into a parallel connection mode, and an amplitude limiting link is added on an additional branch to ensure that the performance of the network following type MMC is kept unchanged during the fault transient state.
2. The control method according to claim 1, characterized in that: the q-axis outer ring constant voltage controller adopts US ref-USThe result is sequentially subjected to an advanced correction auxiliary control link and an outer ring PI controller to obtain an MMC output current q-axis instruction value isqrefAnd then i will besqrefMMC output current d-axis instruction value i generated by d-axis outer ring constant power controllersdrefAs a reference value for the MMC inner-loop current controller, where US refFor grid-connected point voltage reference, USIs the MMC grid-connected point voltage amplitude.
3. The control method according to claim 1, characterized in that: the transfer function expression of the lead correction auxiliary control link is as follows:
Figure FDA0003407092530000011
wherein: gC(s) is the transfer function of the lead correction auxiliary control element, KcIs a gain constant, T and β T are respectively a lead time constant and a lag time constant, β is a lag coefficient, and s is laplacian.
4. The control method according to claim 1, characterized in that: the advanced correction auxiliary control link is formed by connecting an original branch and an additional controller in parallel, namely GC(s)＝GX(s)+1，GC(s) is the transfer function of the lead corrected auxiliary control element, GX(s) is the transfer function of the additional controller, expressed as follows:
Figure FDA0003407092530000012
wherein: kcIs a gain constant, T and β T are respectively a lead time constant and a lag time constant, β is a lag coefficient, and s is laplacian.
5. The control method according to claim 3 or 4, characterized in that: the lead time constant T, lag coefficient beta and gain constant KcThe calculation expression of (a) is as follows:
Figure FDA0003407092530000021
Figure FDA0003407092530000022
Figure FDA0003407092530000023
wherein: omegacIs the dominant angular frequency of oscillation of the generator,
Figure FDA0003407092530000024
the most advanced phase.
6. The control method according to claim 5, characterized in that: the maximum lead phase
Figure FDA0003407092530000025
The calculation expression of (a) is as follows:
Figure FDA0003407092530000026
Figure FDA0003407092530000027
wherein: f. ofcIs the dominant oscillation frequency of the generator, KvAnd TvRespectively a proportional coefficient and an integral coefficient of the outer loop PI controller,
Figure FDA0003407092530000028
for outer loop PI controllers at fcLagging phase provided at the frequency point.
7. The control method according to claim 4, characterized in that: the amplitude limiting link is used for limiting the amplitude of the additional controller, and the output of the additional controller is limited to be-0.02 p.u. to 0.02p.u.
8. The control method according to claim 1, characterized in that: the control method adopts improved reactive constant alternating voltage control, and an advanced correction auxiliary control link is added to a q-axis outer ring controller of a network-following type MMC, so that the phenomenon of low-frequency oscillation instability of a system caused by the access of a traditional network-following type MMC converter station is inhibited, and the synchronous and stable operation of a power supply system and a power grid is ensured; meanwhile, parallel feedforward control is adopted, and an amplitude limiting link is arranged on an additional branch, so that the fault transient operation characteristic of the network-following MMC is guaranteed to be unchanged.
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